The invention pertains to capacitor constructions, methods of forming bitlines, and to methods of forming structures comprising both capacitors and bitlines.
A typical semiconductor dynamic random access memory (DRAM) array will comprise wordlines, bitlines, and capacitor structures. A prior art method of forming a portion of a memory array is described with reference to FIGS. 1-6.
Referring initially to FIG. 1, a semiconductor wafer fragment 10 comprises a semiconductive material substrate 12 having a first insulative material 14 formed thereover. To aid in interpretation of the claims that follow, the terms xe2x80x9csemiconductive substratexe2x80x9d and xe2x80x9csemiconductor substratexe2x80x9d are defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term xe2x80x9csubstratexe2x80x9d refers to any supporting structure, including, but not limited to, the semiconductive substrates described above. Substrate 12 can, for example, comprise a monocrystalline silicon wafer having various circuitry elements (not shown) associated therewith. Insulative material 14 can comprise, for example, borophosphosilicate glass (BPSG).
Conductive plugs 16 are formed to extend through insulative material 14 and to substrate 12. Conductive plugs 16 can comprise any of a number of conductive materials, including, for example, metals and/or conductively doped polysilicon. Conductive plugs 16 can be electrically connected with conductive circuitry that is part of substrate 12, and which is not shown. Plugs 16 can be formed within insulative material 14 by, for example, etching openings in material 14, filling such openings with the conductive material, and subsequently removing any excess conductive material remaining over insulative material 14 by, for example, chemical-mechanical polishing.
A second insulative material 18 is formed over conductive plugs 16 and first insulative material 14. Second insulative material 18 can comprise, for example, silicon dioxide.
A plurality of patterned bitlines 20, 22 and 24 are formed over second insulative material 18. The patterned bitline constructions 20, 22 and 24 comprise a pair of conductive materials 26 and 28, and a third insulative material 30 overlying conductive materials 26 and 28. Conductive materials 26 and 28 can comprise, for example, conductively doped polysilicon and a metal-silicide, respectively. The metal-silicide can comprise, for example, titanium silicide or tungsten silicide. It is noted that although the shown bitlines comprise two conductive materials, the bitlines can also be formed to comprise only one conductive material, or more than two conductive materials. If the bitlines comprise only one conductive material, such conductive material can be either conductively doped polysilicon or a metal silicide. The insulative material 30 of bitline constructions 20, 22 and 24 can comprise one or more insulative layers. Individual layers can comprise, for example, silicon dioxide.
A plurality of insulative spacers 32 are formed along sidewalls of bitline constructions 20, 22 and 24. Insulative spacers 32 can comprise, for example, silicon nitride.
FIG. 2 shows a top view of fragment 10 at the processing step of FIG. 1, and shows bitline constructions 20, 22 and 24 extending as lines across an upper surface of second insulative material 18. FIG. 2 also shows wordline locations 34, 36 and 38 (indicated by dashed lines) extending across fragment 10 perpendicularly relative to bitline structures 20, 22 and 24. Wordlines can be formed in locations 34, 36 and 38 to extend either above or below bitline structures 20, 22 and 24, and accordingly can be formed either before or after the patterning described with reference to FIG. 1.
Referring next to FIG. 3, wafer fragment 10 is shown in a view corresponding to that of FIG. 1, and at a processing step subsequent to FIG. 1. Specifically, a fourth insulative material 40 has been formed over bitline constructions 20, 22 and 24, and a patterned masking layer 42 has been formed over fourth insulative material 40. Fourth insulative material 40 can comprise, for example, a silicon oxide such as, for Example, silicon dioxide or BPSG, and patterned masking layer 42 can comprise, for example, photoresist.
Patterned masking layer 42 has openings 44 extending therein and such openings are transferred through insulative materials 40 and 18 with a suitable etch to extend the openings to conductive plugs 16. Preferably, the etch utilized to extend openings 44 through insulative materials 40 and 18 is an etch selective for materials 40 and 18 relative to spacers 32. However, a difficulty with the etch can be that the etch is not 100% selective for the silicon oxide materials relative to the silicon nitride material, and accordingly if the etch is conducted too long it can etch through the silicon nitride spacers to expose conductive materials 26 and 28. The shown embodiment of FIG. 3 is an idealized etch wherein only insulative materials 18 and 40 have been etched, and wherein spacers 32 have not been etched. It is to be understood that such idealized etch rarely, if ever occurs, and accordingly there is typically at least some etching of insulative spacers 32 during the etch of materials 18 and 40.
FIG. 4 shows a top view of wafer fragment 10 at the processing step of FIG. 3, and shows that openings 44 are preferably formed at locations between bitlines 20, 22 and 24 (shown in phantom), as well as between wordline locations 34, 36 and 38. The processing of FIG. 4 is shown as idealized processing wherein the openings 44 are aligned to be between bitlines 20, 22 and 24. It is noted that occasionally mask S misalignment occurs, and openings 44 are accordingly shifted to extend into one or more of bitline constructions 20, 22 and 24. Such shift can result in exposure of conductive materials 28 and/or 26 during the etch utilized to form openings 44. Such exposure of conductive materials 28 and/or 26 can ultimately result in device failure.
FIG. 5 shows wafer fragment 10 at a processing step subsequent to that of FIG. 3, and in a view corresponding to that of FIG. 3. Capacitor constructions 46 and 48 are formed between and over bitline constructions 20, 22 and 24, and in electrical connection with conductive plugs 16. Capacitor constructions 46 and 48 comprise conductive storage nodes 50 and 52, respectively. Conductive storage nodes 50 and 52 can be formed of, for example, metal and/or conductively doped polysilicon. Capacitor constructions 46 and 48 further comprise a dielectric layer 54 and a conductive capacitor plate 56. Dielectric layer 54 can comprise, for example, silicon dioxide, silicon nitride, tantalum pentoxide, and/or other insulative materials known to persons of skill in the art. Conductive capacitor plate 56 can comprise, for example, metal and/or conductively doped polysilicon.
FIG. 6 shows a top view of wafer fragment 10 at the processing step of FIG. 5, and shows additional capacitor constructions 58 and 60 associated with wafer fragment 10. Constructions 58 and 60 can be similar to constructions 46 and 48 in comprising storage nodes (not shown), dielectric layer 54, and conductive capacitor plate 56. In the shown embodiment, capacitor constructions 46, 48, 58 and 60 extend over wordline locations 34, 36 and 38, as well as over bitlines 20, 22 and 24. Capacitor constructions 46, 48, 58 and 60 are typically electrically connected to transistor gates associated with wordlines 34, 36 and 38, as well as to bitlines 20, 22 and 24. More specifically, each of capacitors 46, 48, 58 and 60 is typically constructed to be selectively addressable by a particular combination of a wordline and a bitline to form an addressable storage unit of a memory device.
The prior art processing of FIGS. 1-6 has problems associated therewith which were discussed with relation to FIGS. 3 and 4. Specifically, mask misalignment at the processing of FIGS. 3 and 4 can expose conductive materials of the bitlines which can ultimately cause a short of the bitlines to capacitor constructions formed adjacent the bitlines, and result in device failure. Further, non-selectivity of the etch utilized to form the openings 44 shown in FIGS. 3 and 4 can result in exposure of conductive materials of the bitlines, and also ultimately lead to shorting of the bitlines to capacitor constructions formed adjacent them, and device failure. The problems become increasingly severe with decreasing bitline spacing due to thinner nitride spacers and tighter mask alignment tolerances. Accordingly, it would be desirable to develop new methods for forming capacitor structures and bitline constructions which avoided the problems.
In one aspect, the invention encompasses a method of forming bitlines. A substrate is provided, and comprises a plurality of spaced electrical nodes. A bitline layer is formed over at least some of the spaced electrical nodes. The bitline layer comprises at least one conductive material. Openings are etched through the bitline layer and to the electrical nodes. After the openings are formed, the bitline layer is patterned into bitlines.
In another aspect, the invention encompasses a method of forming a capacitor and bitline structure. A substrate is provided, and comprises a plurality of spaced electrical nodes. A stack of bitline materials is formed over at least some of the spaced electrical nodes. The bitline materials comprise at least one insulative material over at least one conductive material. Openings are etched through the bit line materials and to the electrical nodes. Conductive masses are formed in at least some of the openings. After the conductive masses are formed, the bitline materials are patterned into bitlines. Capacitor constructions are formed over the patterned bit lines and electrically connected to the electrical nodes through the conductive masses.
The invention also encompasses capacitor constructions.